Implantable medical devices (IMD) provide medical functions to patients. Examples of these functions include defibrillator shocks, muscle and neurological tissue stimulation, and physiological sensing. The IMD device may communicate with an external instrument (EI) such as a device programmer from time to time for various reasons. For instance, the IMD may transfer to the EI data that has been collected over a given period of time. As another example, the EI may transfer stimulation parameter settings to the IMD.
The communications between the EI and the IMD utilize modulation of a carrier signal to convey information. The modulation has various parameters. One parameter is the modulation type which pertains to how the information is represented on the carrier signal. Another parameter is the modulation symbol rate which pertains to how quickly the information is being conveyed by the carrier signal. Conventionally, modulation parameters such as these are fixed because once the modulation parameters are chosen and put into use, they are not subsequently changed.
Communicating with fixed modulation parameters between the IMD and the EI has various drawbacks. For instance, if the communication signals could support a higher symbol rate than what has been chosen at any given point during a communication session, then the communication session will take longer than if a higher symbol rate had been chosen. Likewise, if the communication signals are not adequately exchanged due to a chosen symbol rate being too high at any given point during a communication session, then the session may fail altogether and/or numerous re-attempts may result in the session taking longer than if a lower symbol rate had been chosen.
Similar issues exist for modulation type as well, where a given modulation type may support a higher throughput at a given point in time during a communication session but a less efficient modulation type has instead been chosen which may lead to a longer communication session. As another example, a given modulation type may support a more reliable exchange of information at a given point in time during a communication session but a less reliable modulation type has instead been chosen which may result in a failed communication session and/or a longer communication session.
IMDs have a limited amount of electrical power available in an on-board battery. Sending and receiving information consumes a significant amount of that electrical power. Therefore, exchanges of information between an EI and an IMD are one factor that constrains the length of time that the IMD can operate before exhausting the on-board battery.